The Acorn Atom


The Atom is a Basic oriented computer. The screen is 32 characters wide and 16 characters high. There is no startup beep. The welcome message is:

The character set is upper case only, lower case is printed as reverse upper case. The standard Atom has color commands, but only a monochrome output.

Power supply

The standard Atom uses 8 Volt DC as power supply, internally regulated to 5 Volt. With extra memory installed, this could get problematic. The Technical manual advised to remove the internal regulators and use a 5 Volt external power supply.


Basic is the original programming language of the Atom. Being very different from the standard Microsoft Basic, it has some simularities with the Basic of its successor the Acorn BBC computer. The Basic is capable of integer variables only, floating point was available as extra ROM, for which a socket was available inside. Another socket is available for other applications. It was mainly used for toolkits (third party). The sockets accept only ROMs and 2532 EPROMS (4kx8).

On cassette several other languages were available like Lisp and Forth.


The Atom memory can be extended internally with 2114 (1kx4) memory chips. There was room for one Euro extension card internally and a connector for external expansion. A Centronics printer could be connected, but only if an optional 6522 VIA chip was installed.

A Disk pack for the Atom was available, using 5 1/4," single density, single sided floppy disks. The controller board added a Floppy Disk Controller (8272), a DOS Rom and extra memory to the Atom. The power supply in the pack could also power the Atom. As the whole disk operating system is on ROM, the disk is only used for storage.

Some commands:

enters the DOS. The LOAD and SAVE commands apply now to disk, not cassette. Use the BREAK key to return to the cassette basic.
load the directory information into a buffer (but does not show it). This is a sort of mount command.
prints the directory information from the buffer on the screen. If the disk was spinning, an implicit *DIR is executed.

Other official extensions are a colour board, 40x24 VDU board and a BBC Basic board.

The Atom was extended by hobbyists to great extend. Some of it was inspired by the ROM switching capability of the BBC computer. Some of the other additions were a Double Density Disk Controller (combined with CP/M support), 80x24 VDU.


F.J. Kraan, 2004-05-02